linux-kernel - Re: [v3 1/4] ARM: dma-mapping: atomic

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Message-ID: <20120824.145200.843951079622652894.hdoyu@nvidia.com>
Date:	Fri, 24 Aug 2012 13:52:00 +0200
From:	Hiroshi Doyu <hdoyu@...dia.com>
To:	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>
CC:	"m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kyungmin.park@...sung.com" <kyungmin.park@...sung.com>,
	"arnd@...db.de" <arnd@...db.de>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"chunsang.jeong@...aro.org" <chunsang.jeong@...aro.org>,
	Krishna Reddy <vdumpa@...dia.com>,
	"subashrp@...il.com" <subashrp@...il.com>,
	"minchan@...nel.org" <minchan@...nel.org>,
	"pullip.cho@...sung.com" <pullip.cho@...sung.com>
Subject: Re: [v3 1/4] ARM: dma-mapping: atomic_pool with struct page **pages

Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> wrote @ Fri, 24 Aug 2012 13:13:23 +0200:

> On Fri, Aug 24, 2012 at 11:29:02AM +0300, Hiroshi Doyu wrote:
> > struct page **pages is necessary to align with non atomic path in
> > __iommu_get_pages(). atomic_pool() has the intialized **pages instead
> > of just *page.
> > 
> > Signed-off-by: Hiroshi Doyu <hdoyu@...dia.com>
> > ---
> >  arch/arm/mm/dma-mapping.c |   17 +++++++++++++----
> >  1 files changed, 13 insertions(+), 4 deletions(-)
> > 
> > diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> > index 601da7a..b14ee64 100644
> > --- a/arch/arm/mm/dma-mapping.c
> > +++ b/arch/arm/mm/dma-mapping.c
> > @@ -296,7 +296,7 @@ struct dma_pool {
> >  	unsigned long *bitmap;
> >  	unsigned long nr_pages;
> >  	void *vaddr;
> > -	struct page *page;
> > +	struct page **pages;
> >  };
> >  
> >  static struct dma_pool atomic_pool = {
> > @@ -335,12 +335,16 @@ static int __init atomic_pool_init(void)
> >  	unsigned long nr_pages = pool->size >> PAGE_SHIFT;
> >  	unsigned long *bitmap;
> >  	struct page *page;
> > +	struct page **pages;
> >  	void *ptr;
> >  	int bitmap_size = BITS_TO_LONGS(nr_pages) * sizeof(long);
> > +	size_t size = nr_pages * sizeof(struct page *);
> >  
> > -	bitmap = kzalloc(bitmap_size, GFP_KERNEL);
> > +	size += bitmap_size;
> > +	bitmap = kzalloc(size, GFP_KERNEL);
> >  	if (!bitmap)
> >  		goto no_bitmap;
> > +	pages = (void *)bitmap + bitmap_size;
> 
> So you stuck a bitmap field in front of the array then?
> Why not just define a structure where this is clearly defined
> instead of doing the casting.

I just wanted to allocate only once for the members "pool->bitmap" and
"pool->pages" at once. Since the size of a whole bitmap isn't known in
advance, I couldn't find any fixed type for this bitmap, which pointer
can be shifted without casting. IOW, they are variable length.
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